noun an interval containing an octave and a second.
2. ninth ·noun a chord of the dominant seventh with the ninth added.
3. ninth ·adj following the eight and preceding the tenth; coming after eight others.
4. ninth ·adj constituting or being one of nine equal parts into which anything is divided.
5. ninth ·noun the quotient of one divided by nine; one of nine equal parts of a thing; the next after the eighth.